What are held together in a tough fibrous structure known as a capsule

Joints.

---> Joints are held together in a tough fibrous structure known as a capsule.

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You did not show us the image of the burger, but i shall try to answer as best i can.  when purchasing food, always consider the ingredients as well as the person who prepared it. consider if they were hygienic people or not, in case the burger was infected with bacteria. no mortal should place an infected burger into their mouth.